Comprehensive Guide to Upgrading from JDK8/11 to JDK17: Performance Benefits, New Language Features, and Migration Steps

If you are still on JDK 8 and have encountered OutOfMemoryError or JVM tuning issues, this guide introduces a garbage collector that can deliver hundred‑fold performance improvements and helps you decide whether to upgrade to JDK 17.

01. Introduction

During an agile team building exercise, the author explored Suite executors for unit testing and began a deeper investigation into JDK upgrades.

02. Why Upgrade to JDK 17

JDK 17 is a long‑term support (LTS) release from Oracle (September 2021) that ensures stable updates and reliability.

Performance improvements : G1GC speed up 8.66 % and ParallelGC 6.54 % from JDK 11 to JDK 17; the stable ZGC offers sub‑millisecond pause times.

New syntax and features : switch expressions, text blocks, pattern‑matching instanceof, improved NPE messages, and more.

Framework support : Spring Framework 6 and Spring Boot 3 require at least Java 17.

03. Benchmark Results

Benchmarks on JDOS platform with machines 2C4G, 4C8G, 8C16G using JDK 8, JDK 11, and JDK 17 show clear GC performance gains, especially with ZGC.

04. Oracle JDK vs OpenJDK

Since JDK 11 the functional differences have vanished; OpenJDK 17 or other community builds (AdoptOpenJDK, RedHat OpenJDK) are recommended.

05. JVM Improvements

Key changes from JDK 11 to JDK 17 include:

ZGC is now a production feature (enable with -XX:+UseZGC ).

G1GC enhancements (abortable mixed collections, NUMA‑aware allocation).

Removal of CMS GC (JDK 14) and deprecation of ParallelScavenge + SerialOld.

Bias locking disabled by default (JDK 15).

Enhanced NPE messages that pinpoint the exact null variable.

05.2 New Language Features

Switch expressions simplify branching with -> syntax.

Text blocks allow multi‑line strings using """ to reduce escaping.

Records (JDK 14) provide immutable data classes without boilerplate.

Pattern‑matching instanceof removes the need for explicit casts.

Sealed classes/interfaces (JDK 15) restrict which types can extend or implement them.

06. Migration Steps

Upgrade JDK version, adjust Maven compiler settings:

<properties>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
</properties>

Upgrade Spring Boot to 2.7.15 (keep compatibility with Java 17) and adjust parent POM:

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.7.15</version>
</parent>

If circular dependencies appear, either refactor beans or enable them via:

spring.main.allow-circular-references=true

For Swagger incompatibility with Spring Boot 2.7, add the following bean post‑processor:

@Bean
public BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
    return new BeanPostProcessor() {
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) {
            if (bean instanceof WebMvcRequestHandlerProvider || bean instanceof WebFluxRequestHandlerProvider) {
                customizeSpringfoxHandlerMappings(getHandlerMappings(bean));
            }
            return bean;
        }
        private
void customizeSpringfoxHandlerMappings(List
mappings) {
            List
copy = mappings.stream()
                .filter(mapping -> mapping.getPatternParser() == null)
                .collect(Collectors.toList());
            mappings.clear();
            mappings.addAll(copy);
        }
        private List
getHandlerMappings(Object bean) {
            try {
                Field field = ReflectionUtils.findField(bean.getClass(), "handlerMappings");
                field.setAccessible(true);
                return (List
) field.get(bean);
            } catch (Exception e) {
                throw new IllegalStateException(e);
            }
        }
    };
}

When upgrading middleware, add required module opens/export flags, e.g.:

--add-opens java.base/java.lang=ALL-UNNAMED
--add-exports java.base/sun.security.action=ALL-UNNAMED

For AKS, add JAXB dependencies because Java 11 removed Java EE modules:

<dependency>
    <groupId>jakarta.xml.bind</groupId>
    <artifactId>jakarta.xml.bind-api</artifactId>
    <version>2.3.2</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jaxb</groupId>
    <artifactId>jaxb-runtime</artifactId>
    <version>2.3.2</version>
</dependency>

07. Summary

Upgrading to JDK 17 unlocks sub‑millisecond GC pauses, modern language features, and long‑term support; the migration is straightforward but requires updating middleware versions, Maven/Gradle settings, and adding appropriate JVM arguments for reflective access.